1. Field of the Invention:
The invention relates to electric motor armature constructions and methods of winding related thereto.
2. Description of the Prior Art:
Electric motor armature winding typically involves placing and securing the windings in the core slots and making appropriate winding connections to the commutator bars. In the so-called tang method of winding, the commutator is provided with tangs about which the windings are looped prior to being fused to the appropriate commutator bars. Another basic system of winding an armature with a slotted core and a commutator is the lead loop method in which the commutator is formed without tangs. A comparison of the conventional tang method and lead loop method will next be described.
In the tang method of winding, the winding operation starts after the armature and shaft have been assembled with a commutator having the appropriate number of tangs corresponding to the number of commutator bars. The slotted core is then wound with a tang-type winding machine which places the coil ends on the appropriate tangs as part of the coil winding operation. Wedges are placed in the core slots to secure the windings and the tangs are bent and heated which mechanically crimps and electrically connects the coil ends to the respective tangs and also burns away the insulation at the points of connection. The armature is then impregnated with an appropriate insulating material after which the commutator is turned to the finish size.
The tang winding method has a number of advantages as compared to the lead loop winding method. With the tang method, the coil ends are connected mechanically to the commutator bars. There is generally less scrap as compared to the lead loop method. The tang winding method also involves less opportunity for connection errors, provides an armature which is easier to balance than is an armature wound by the lead loop method and generally requires less production time than is required with the lead loop method. However, the tang winding method generally produces an armature with a life expectancy which is less than the life expectancy to be expected from an armature of comparable electrical character wound by the lead loop method. The tang-type winding method also inherently makes connections between the coil ends and the tangs having relatively high electrical resistance. Also, the tangs tend to bend out of alignment and this produces poor electrical connections. The presence of the tangs also tends to increase the overall diameter of the commutator which may be a material disadvantage when a minimum commutator outside diameter is desired and as might be obtained with the lead loop method.
Comparing the lead loop winding method with the tang winding method, the winding operation starts by providing an armature fitted with a slotted core and a shaft but without a commutator. The slotted core is wound with a lead loop-type winder following which the loose coil ends are twisted by the operator around the armature shaft. Wedges are then installed in the armature core slots with a wedge machine after which the operator unwinds and spreads the coil ends. The commutator which is formed without tangs but with individual commutator bar slots is installed on the armature shaft. The leading coil ends are then placed in proper sequence in the individual commutator bar slots and are mechanically staked which mechanically secures the respective coil ends to the respective commutator bars. The staking operation also severs the excess wire on the coil ends which becomes scrap. The respective coil ends are then fused to the respective commutator bars following which it is customary to tie a cord around the lead ends for mechanical support. The wound armature is then impregnated with an appropriate insulating material following which the commutator is turned to the finish size.
Several advantages of the lead loop winding method have been recognized. A more durable and, therefore, an armature with a higher life expectancy, as compared to a tang-type wound armature, is obtained. The fused commutator bar connections introduce less electrical resistance at the commutator bar connections and therefore are to be preferred over the purely mechanical-type electrical connection achieved in the tang-type winding method. The lead loop winding method also allows the outside diameter of the commutator to be reduced by eliminating the tangs. However, there are a number of known disadvantages attributable to the lead loop winding method. The lead loop winder, for example, typically produces scrap at a relatively high rate. A relatively high labor content is also involved in the lead loop winding method because of the added operation associated with handling the loose coil ends after the armature core has been wound and before the commutator bars are connected. The lead loop winding method also inherently introduces a substantial opportunity for connection error and this leads to an increase in the number of armatures that have to be scrapped because of connection errors. Finally, it can be observed that the lead loop winding method inherently requires use of excess wire for the purpose of providing operator identification of the particular coil ends to be connected to the particular commutator bars.
With the above as background, the object of the invention becomes that of providing an armature having a commutator constructed with a temporary tang structure which can be employed during winding so as to preserve all of the advantages of the tang-type winding method and which can be removed after the core has been wound and the commutator bars fused to the appropriate coil ends so as to produce a lead loop-type wound commutator as the end product.